1、 Collection of SANS standards in electronic format (PDF) 1. Copyright This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. This document may reside on a CENTRAL FILE SERVER or INTRA
2、NET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies or organizations. Doing so would constitute a VIOLATION of SABS copyright rules. 2. Indemnity The South African Bureau of Standards accepts no liability for any
3、damage whatsoever than may result from the use of this material or the information contain therein, irrespective of the cause and quantum thereof. ICS 83.060 ISBN 0-626-14427-2 SANS 11346:2003Edition 1ISO 11346:1997Edition 1SOUTH AFRICAN NATIONAL STANDARD Rubber, vulcanized or thermoplastic Estimati
4、on of life-time and maximum temperature of use from an Arrhenius plot This national standard is the identical implementation of ISO 11346:1997 and is adopted with the permission of the International Organization for Standardization Published by Standards South Africa 1 dr lategan road groenkloof pri
5、vate bag x191 pretoria 0001 tel: 012 428 7911 fax: 012 344 1568 international code + 27 12 www.stansa.co.za Standards South Africa 2003 SANS 11346:2003 Edition 1 ISO 11346:1997 Edition 1 Table of changes Change No. Date Scope National foreword This South African standard was approved by National Com
6、mittee STANSA TC 5140.17, Rubber and rubber products, in accordance with procedures of Standards South Africa, in compliance with annex 3 of the WTO/TBT agreement. IS0 11346:1997(E) Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodi
7、es (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations
8、, governmental and non-governmental, in liaison with ISO, also take part in the work. IS0 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated
9、 to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. International Standard IS0 11346 was prepared by Technical Committee lSO/TC 45, Rubber and rubber products, Subcommittee SC 2, Physical and degradation t
10、ests. 0 IS0 1997 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for St
11、andardization Case postale 56 l CH-1211 Geneve 20 l Switzerland Internet central iso.ch x.400 c=ch; a=40Onet; p=iso; o=isocs; s=central Printed in Switzerland ii IS0 ISO11346:1997(E) Introduction With rising temperature, the reaction rate of a chemical reaction is normally increased. For many organi
12、c- chemical reactions a temperature rise of 10 “C means about 2 to 3 times higher reaction rate. The temperature dependence of chemical reactions can be described by the Arrhenius equation: where K(T) = reaction rate constant (min-) A = pre-exponential factor (miti) E = activation energy (J/mol) R =
13、 gas constant (8,314 J/mol K) T = absolute temperature (K) The state of a chemical reaction is given by the relation: F,(t)=K(t)d (1) (2) F,(t) = function of the state of the reaction x t = reaction time (min) Due to different reaction rates Ki at different temperatures Ti the same threshold value F
14、,of a reaction will be reached by different reaction times ti (equal-value times), e.g. tI to t3 in figure 1: Fa (ti)=Ki(%)*ti (3) The Arrhenius equation (1) can be substituted in equation (3) as follows: Fa(ti)=A.e-ER ati (4) or in logarithmic form with the constant terms combined in B In ti =E/R3
15、+B 0 A plot of In t versus l/T gives a straight line with the slope E/R, and is known as an Arrhenius plot (see figure 2). The Arrhenius plot is however normally presented with log 1o time against ITT. The activation energy is constant over a temperature range in which the main ageing reaction is th
16、e same. For extrapolation of short-time data to predict long-term performance, an appropriate curve must be drawn through the short-time values. Caution must be used when the results are analysed. Thermal-oxidative ageing is diffusion-controlled and thus different results can be achieved when compar
17、ing thin and thick test pieces. The ageing reactions can also differ at different temperatures and can affect the property being measured, especially where it is influenced by the balance between scission and cross-linking reactions. The test conditions in the laboratory may also differ from service
18、 conditions where other causes of deterioration such as light ageing and ozone attack may be involved. During the preparation of this International Standard account was taken of the contents of IS0 2578 and IEC 216. This page intentionally left blank INTERNATIONAL STANDARD IS0 IS0 11346: 1997(E) Rub
19、ber, vulcanized or thermoplastic - Estimation of life-time and maximum temperature of use from an Arrhenius plot 1 Scope This International Standard describes the principles and procedures for estimating the life-time and maximum temperature of use of vulcanized or thermoplastic rubbers, using an Ar
20、rhenius plot. This method is suitable for different tests on rubber, but for tests under stress or deformation (creep, relaxation, etc.) physical (viscoelastic) changes of material cannot easily be separated from any chemical change. Then the Arrhenius equation is no longer the only possible model,
21、and the Willams, Landel, Ferry (WLF) equation may be more suitable to represent the change in the material as a function of time. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time
22、 of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 mainta
23、in registers of currently valid International Standards. IS0 188:-l, Rubber, vulcanized - Accelerated ageing and heat-resistance tests. IS0 471: 1995, Rubber - Temperatures, humidities and times for conditioning and testing. IS0 257811993, Plastics - Determination of time-temperature limits after pr
24、olonged exposure to heat. IEC 216 (all parts), Guide for the determination of thermal endurance properties of electrical insulating materials. 3 Definitions For the purposes of this International Standard, the following definitions apply: 3.1 life-time: The time at which the material under test has
25、reached the specified threshold value for the property tested at the temperature of use. 3.2 maximum temperature of use: The temperature at which the material under test has reached the specified threshold value for the property tested after the specified time. 3.3 threshold value: The value specifi
26、ed for the property or change in property being tested . ) To be published. (Revision of IS0 188:1982) IS0 11346: 1997(E) IS0 4 Principle 4.1 At a chosen test temperature, the variations in the numerical value of a chosen property, for example a mechanical or viscoelastic property, are determined as
27、 a function of time. The testing is continued until the relevant threshold value of that property has been exceeded, so that the time limit for that particular temperature of ageing can be determined. Further tests are done at at least two other temperatures. 4.2 The time limits obtained are plotted
28、 on an Arrhenius plot as a function of the straight line obtained is extrapolated back to the temperature of use. temperature, and the 4.3 Although the extrapolation can be made to extremely long times, consideration must be given to the possibility that the chemical reaction at high temperatures is
29、 gradually replaced by a different reaction at lower temperatures. In such a case, the degradation curve will normally deviate from linearity. Because of these considerations, extrapolations are often limited to 30 “C to 40 “C beyond the last data point. If a longer extrapolation is needed, the grea
30、ter uncertainty in the results must be appreciated. 5 Selection of test The test chosen should preferably relate to a property which is likely to be of significance in practice. Wherever possible, use should be made of methods of test specified in International Standards. The following properties ar
31、e often used: tensile strength, elongation at break, stress relaxation in compression or tension, compression set, tension set and tension creep. 6 Selection of threshold value The threshold value should be chosen to suit the conditions of use. A change to 50% of the initial value of the property un
32、der investigation is often used. For properties like compression set and stress relaxation, a value not exceeding 50% is often used. 7 Test pieces 7.1 The dimensions and method of preparation of the test pieces shall be in accordance with the specifications given for the relevant test method. 7.2 Th
33、e total number of test pieces needed depends on: a) the number of test pieces required for the relevant test method; b) the number of time-tests to be made to find the threshold value at a chosen temperature; c) the number of test temperatures; d) the number of control tests with reference test piec
34、es to be made at every heating period. It is advisable to age more than the minimum number of test pieces required, in case problems occur after several weeks, months or years of ageing. 7.3 The tests can often be done with logarithmic time intervals, for example 1 day, 2 days, 4 days, 1 week, 2 wee
35、ks, 4 weeks, 8 weeks, 16 weeks, 32 weeks, etc. Logarithmic time intervals can however be inappropriate for thermal-oxidative ageing, for chemical relaxation and for autocatalytic reactions, where closer test intervals may be needed. IS0 IS0 11346:1997(E) 7.4 When measuring compression set, tension s
36、et and relaxation, the tests are preferably done on the same test pieces, at the different times, to reduce the number of test pieces needed. This also reduces variations in the test results. 8 Temperature of test 8.1 Selection of the test temperatures involves knowing beforehand the approximate age
37、ing characteristics of the material under test. With no previous knowledge of the material, exploratory tests must be made. This information will assist in selecting the test temperatures best suited for the evaluation of the material. 8.2 Test pieces shall be tested at not fewer than three temperat
38、ures, covering a range adequate to establish the life-time estimation by extrapolation with the required degree of accuracy. The lowest test temperature shall be chosen so that the time taken to reach the threshold value is at least 1000 h. Likewise, the highest temperature shall be chosen so that t
39、he time taken to reach the threshold value is not shorter than 100 h. The temperatures used should preferably be standard test temperatures taken from IS0 471. 9 Ageing ovens 9.1 An ageing oven meeting the requirements of IS0 188 shall be used. When tes ts are made in particular medium used. media o
40、ther than air, the method of temperature control shall be adapted to the 9.2 When the tests are made in air, ovens with a known air exchange rate and a known air speed shall be used. Air speed and air exchange rate shall be adequate to ensure that the rate of thermal deterioration is not influenced
41、by accumulated products or evaporated components, or by oxygen depletion. Too high an air speed has been shown to increase deterioration caused by increased oxidation and volatilization of antioxidants and softeners. 9.3 Due to the risk of cross-contamination between test pieces of different rubber
42、materials, use separate ovens or cells for each material. IO Procedure 10.1 At the beginning of the test procedure, make the reference test run with the required number of test pieces, conditioned and tested in accordance with the appropriate standard test method. 10.2 Place the required number of t
43、est pieces in each of the ovens maintained at the selected temperatures. 10.3 At the end of each heating period, condition, if necessary, the test pieces to be examined under the appropriate controlled conditions and then carry out the tests by the previously chosen methods. 10.4 Continue this proce
44、dure until the numerical value of the property under investigation exceeds the relevant threshold value. IS0 11346:1997(E) IS0 11 Expression of results Il.1 To facilitate the determination of the time at which the threshold value is reached, plot the results to give a curve of value of the selected
45、property against time. Determine the values tI, t2, t3, l a9 by interpolation. An example of such a graph is shown in figure 1. 11.2 Plot the log time at which the threshold value is reached for each of the test temperatures against the reciprocal ITT of the corresponding temperature (T = absolute t
46、emperature in K). Construct a best-fit straight line through the plotted points. This may be done using established statistical methods. If a straight line is not appropriate, carry out further tests at other, intermediate, temperatures. If a straight line is still not appropriate, the approach shal
47、l be abandoned. Life-time: Extrapolate the line obtained to the temperature of use giving the life-time estimation. An example of such a plot is given in figure 2. Maximum temperature of use: Extrapolate the line obtained to the specified time giving the maximum temperature of use estimation. 20 000
48、 h is often used as the time for establishing a general maximum temperature of use. 12 Test report The test report shall include the following information: a) a reference to this International Standard; b) sample details: 1) complete identification of the material tested, 2) dimensions and method of
49、 preparation of the test pieces, with reference to the relevant IS0 standard, 3) selected property, with reference to the relevant IS0 standard, 4) threshold value of the selected property, 5) times and temperatures for conditioning of test pieces; c) ageing details: 1) oven type(s) used, with details of air exchange rate and air speed, 2) times and temperatures of exposure in the ovens, 3) precise details of the ageing conditions; d) test results: 1) graphs plotted as specified in 11 .I and 11.2, 2) life-time prediction temperature of use at a at a chosen test tempe cho
